Airships, which may also be referred to as blimps, aerostats, dirigibles, lighter-than-air vehicles, and high-altitude airships, have a gas impervious envelope that contains a volume of lifting gas, such as helium. The envelope typically comprises various sections of fabric that are joined by various seams. Because of the size of the airship, the number of seams required are significant.
One type of prior art seam commonly used to form the envelope of most airships is a butt-joint seam, generally referred to by the numeral 10 as shown in FIG. 1 of the drawings. The butt-joint seam 10 has been found to have acceptable durability, and resiliency to accommodate the operating requirements of the airship. The butt-joint seam 10 is formed by providing at least a first and a second opposed sections of fabric 12 and 14, having opposed edges that are positioned adjacent one another so that they abut or so that they are slightly spaced apart so as to form a joint area 15. Alternatively, the fabric edges 12 and 14 may slightly overlap one another to form the joint area 15, however such arrangement is typically avoided. Each of the fabric sections 12 and 14 may be comprised of a straight ply 16A,16B and a film/bias ply 18A,18B that are adhesively laminated together. As used herein, the A suffixes are associated with fabric section 12 and the B suffixes are associated with fabric section 14. When incorporated into the airship, the straight plies 16A,16B face the interior volume of the envelope, while the film/bias ply 18A,18B face the external environment. Moreover, each of the fabric sections 12,14 provide an outer and an inner bonding surface 20 and 22 respectively. The fabric sections 12 and 14 are joined using an adhesive carrying cover tape 24 and an adhesive carrying seam tape 26, which are adhesively laminated to the outer bonding surface 20 and the inner bonding surface 22 respectively. In other words, the cover tape 24 is adhesively disposed upon the outer surface 20, while the seam tape 26 is applied to the inner surface 22 in a laminated manner. The seam tape 26 distributes loads resulting from forces applied to the seam 10, while the cover tape 24 is provided to protect the exposed edges of the straight plies 16A,16B and the film/bias plies 18A,18B in the joint area 15 from environmental forces, such as UV radiation, while enhancing the lifting gas retention properties of the envelope. Moreover, the outer surface 20 of the film/bias plies 18A,18B, and the cover tape 24 maintain an aluminum coating that serves to reduce the permeability of the lifting gas through the seam 10, and the fabric sections 12,14 that make up the envelope of the airship.
While the butt-seam 10 discussed above utilizes a single seam tape 26, it is advantageous to further increase the strength and durability of the seam 10. One manner to achieve this increased strength, is by replacing the cover tape 24 with another section of seam tape 26, to form a double tape butt joint seam. Unfortunately, the utilization of a second seam tape 26 upon the film/bias plies 18A,18B would not add any appreciable strength to the seam 10, as the film/bias plies 18A,18B to which the second seam tape would be attached is not a load carrying member of the seam 10 in the principal load carrying directions (hoop and axial) of the airship. Therefore, a designer of an airship using conventional seam arrangements is generally limited to the strength achieved by use of a butt-joint that utilizes a single seam tape 26.
Additionally, when the butt-seam 10 is used to join large sections of fabric as in the formation of the airship envelope, significant amounts of seamed area are generated, which due to the use of the structural tape 26, and cover tape 24, imparts unwanted weight to the airship. Further, because the seam tape 26 of the butt-seam 10 is only applied to the inner surface 22 of the fabric sections 12,14 when the butt-seam 10 is formed, loads applied to the seam 10 are distributed across the inner surface of the seam in an unbalanced manner. In addition, because of the unbalanced distribution, the surface of the butt-seam 10 generates stress concentrations, without providing backup for flaws that may exist in the adhesion interface between the joined fabric sections 12,14 about the joint 15.
Therefore, there is a need for a splice seam that does not utilize a seam tape or a cover tape, or eliminates just the cover tape so as to reduce the weight of the seam. Additionally, there is a need for a splice seam that is able to distribute forces from an applied load uniformly across the joint of the splice seam. Furthermore, there is a need for a splice seam that has reduced stress concentrations when a load is applied thereto. Still yet, there is a need for a splice seam that has reduced helium permeability.